1. Field of the Invention
The present invention generally relates to a fuel vapor treatment system. More specifically, the present invention relates a fuel vapor treatment system equipped with a failure diagnosis device.
2. Background Information
An example of a fuel vapor treatment system is described in Japanese Laid-Open Patent Publication No. 07-317611. This fuel vapor treatment system has an absolute pressure sensor installed in the evaporation passage that communicates between the fuel tank and the canister. By measuring the atmospheric pressure as a reference pressure, this fuel vapor treatment system diagnoses leaks inside the fuel vapor treatment system based on the difference between the reference pressure and the pressure inside the evaporation passage.
In view of the above, there exists a need for an improved fuel vapor treatment system. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
The fuel vapor treatment system just described requires the installation of two sensors, i.e., an absolute pressure sensor and an atmospheric pressure sensor, and thus invites higher cost.
If the atmospheric pressure sensor is eliminated, the pressure inside the fuel vapor treatment system will fluctuate when the engine is started because of negative pressure inside the intake manifold. This creates a problem in that, during the fluctuation, it cannot be determined if the pressure value detected by the absolute pressure sensor is normal or if it is the pressure obtained when the drain cut valve provided on the canister is stuck in the closed state.
Furthermore, if one attempts to measure the reference pressure after the engine is started and the drain cut valve happens to fail such that it is stuck in the closed state, negative pressure inside the intake manifold will cause negative pressure inside the purge pipe and it will not be possible to set the reference pressure.
Therefore, the object of the present invention is to provide a fuel vapor treatment system that diagnoses failure of the drain cut valve and solves the aforementioned problems.
In accordance with the present invention, a fuel vapor treatment system is provided that basically comprises a fuel tank, a canister, a purge valve, a sensor and a failure diagnosis device. The canister is fluidly coupled to the fuel tank by a first pipe and configured to adsorb fuel vapor evaporated from the fuel tank. The drain cut valve is operatively coupled to the canister to control air flow into the canister. The purge valve is disposed in a second pipe fluidly coupled between the canister and an intake passage of an internal combustion engine into which fuel vapor flows from the canister. The sensor is configured and arranged to detect absolute pressure inside at least one of the first and second pipes. The failure diagnosis device is configured and arranged to set a reference pressure used for failure diagnosis of the drain cut valve while the purge valve is closed.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.